What my last mono partner wanted/needed.
The last poly relationship that I was in with a monogamous man taught me a lot about taking care of two hearts/individuals. I swiftly learned that while I loved both people very much, my primary partner's wishes and needs had to be of the utmost importance to me in order for him to feel comfortable with something that was a very foreign concept to him (he had never even heard of polyamory before).
We had a lot of ground rules that we established TOGETHER:
1) I went and saw my secondary partner on weekends when my primary was out of town/had plans. If my primary partner's plans changed and he was going to be home, he had the right to "veto" my time and ask me to cancel plans with my secondary (he rarely if ever did this, but I think that was partly due to the fact that he knew he had the option to)
2) I was never allowed to bring my secondary to our house when he was home, and we were never allowed in "our bed" - only the spare bedroom.
3) He didn't want to know about most things. I respected that.
4) I was responsible for "coming down" from my weekends with my secondary by myself - I would usually take time to do yoga, meditate, have a bath, read, or journal and "get out" the last of my NRE for my secondary and be ready to bring my attention and energy back to my primary.
5) When I did need to talk about something that was happening with my secondary with my primary, I let him know that I needed to talk with him, and he let me know when he was ready (emotionally, mentally, etc) We'd then talk about proposed dates/scheduling (Valentine's Day, for example - or when my secondary's wife and him were having problems and I didn't know what to do)
6) They never met. He never wanted to meet him. He didn't want me to go into any kind of details about my life with my secondary ever, unless we were having a serious talk. I respected that.
Our rules worked for us. We talked a lot about our relationship, and established boundaries and rules/talked about opening up our relationship for almost a year before it actually happened.
My heart goes out to you about being cheated on; she is lucky you are willing to stand by her during this time. My advice is always the same: Be Honest, Communicate, Stand Up For Yourself, Follow Your Heart, Demand Respect if You Have To, Don't Be Afraid to Have Conflict, Take Time For Yourself, Talk to Someone You Trust (this forum def. counts!)
You seem like a wonderful, emotionally rich man. Do NOT feel bad about wanting her to see him on Mondays - I think that is a totally reasonable request. This has to work for both of you, and YOU can't be the only one making compromises and concessions - she needs to work on making this comfortable and doable for you as well!