Hi, Silia! I've been following your story since the beginning. At one point or another most of us have been in your shoes. Let me congratulate you on being willing to explore who you are and seeking some advice. It's a huge step. I'm glad the talk with your boyfriend went well. It make not seem like it, but that is one of the most positive reactions that can realistically be expected. I hope as your love and relationship continue to grow and strengthen that he will be willing to try opening up to the possibilities that non-monogamy provide. *fingers crossed*
We, as people, are taught to fear the unknown, and too often we formulate opinions without adequate knowledge of a subject. Knowledge is a powerful thing. I would suggest having him look at some threads on this site to get a better understanding of polyamory and non-monogamy in general. It may help him understand that it isn't a matter of loving him less, but wanting to love more. Remember that this is a learning and growing experience for him as much as it is for you.
Remember that there is no need to rush things; just take them as they come. I have found that many stresses in a relationship are caused by arbitrary deadlines that we create. You guys are young. You have all the time in the world. In my own relationship has become infinitely happier and stronger since I learned to stop rushing towards the destination I have imagined for us. Life is truly in the journey, and I realized that I was pushing so fast and so hard that I was missing all these beautiful opportunites to live and love and grow together. I was missing what made us a couple, what made me want to be with him for the rest of my life. My advice: don't rush, be true to yourself, and enjoy every moment. And remember that adding more people adds the potential for more drama and more frustration, but also the potential for more love and more opportunities to make memories.
Oh, I almost forgot the reason I originally wanted to post.
It's mostly just that I generally need a lot of wind up, a night out, sexy clothes, that kind of stuff to get in the mood, because it can be really hard for me right now. After a night out, however, he generally just likes to crash out.
Lack of sex has the potential to be a huge issue in your relationship, especially if you are starting to explore polyamory. Honest communication and consideration for your partner(s)'s feelings are two of the most important things for making any relationship work. These get exponentially more important with each person added. With regard to your boyfriend's feelings, you have to try to understand what your desire to possibly explore non-monogamy makes him feel. Feelings of inadequacy are very common. (Ie. "If I was enough then she wouldn't want anyone else, right?") This is going to be doubly important if he feels the amount of sex you have is low. ("She doesn't want to have sex with me, but she wants to do it with other guys. What's wrong with me? What am I doing wrong?) I could go on forever about every possible thought and worry that might cross his mind.
The key is to listen to your own heart and his. Talk about things. You truly need to work on your relationship with him, dealing with any concerns and issues before adding more people. Remember that this is the man you love. You don't want to lose him just to see how things may play out with another. Strengthen you bonds. Make him feel loved and desired. A relationship is like a building: you need a strong foundation before you add more floors (whether kids or additional partners), otherwise it will be unstable and prone to collapse.
As for trying to deal with the physical aspects of showing that you love and desire him, have you tried any other ideas to get you in the mood more often? It sounds like you aren't opposed to more sex (I know people who are), but simply that your libido isn't cooperating. Most women need hours of mental stimulation to really ramp up, which is probably why a night out all dressed to the nines is what you need. I would suggest doing a few things to kickstart the same feeling earlier in the day. Perhaps wear sexy underwear to work or write down a fantasy on your lunch break. I'm personally a huge fan of sexting, as it plants the idea and has you anticipating the follow through for hours. By the time I get home I'm practically ready to tear my boyfriend's clothes off. I also find that planning a romantic interlude for him turns me on and is something I can do throughout the day. As cheesy as it sounds I get all dolled up, put on some soft music, a little candle light, and a massage. All done to relax him and show how much I love him, with no pressure for sex on either of us. Sometimes he's so relaxed he falls asleep. Sometimes I'm feeling so relaxed and sensual that I naturally roll it into sex. Definitely win-win! I also loved Nycindie's advice on keeping the evening's activities shorter so that he doesn't run out of steam on you when you are trying.
All of these things work really well for us. There are a bunch of websites and articles to give you ideas if you want to try them. Let me know and I'll post some links. I hope this helps and apologize for any repetition of other posts! Best of luck!