Jealousy is always about fear of losing something, regardless of whether it's realistic or not. Sometimes it's fear of losing love, sometimes of losing control, and sometimes things from our past can crop up -- our current situation can be a trigger for a past loss that we don't want to think about.
While it's very true that jealousy is YOUR emotion to own and figure out how to deal with, our lovers can help us by listening, providing reassurance that they are there for us, and answer questions that we need to ask them.
First steps into poly are always big ones -- there really is no other way to deal with the emotional impact of sharing a partner until we are in the situation. It's very much like being thrown into the water and having to figure out how to swim -- or sink.
Like learning to swim, we can't really figure it out ahead of time from reading a book or hearing how other people did it. We pretty much have to get in the water and DO it. Once you're in there, though, it does help a lot to have someone right there beside us to grab onto us if we start to sink, or feel scared.
Go easy on yourself, and also try not to get angry at your partner. If you can, try not to take away things you have already granted to your partner, such as the freedom to see her boyfriend. Asking for more time for yourself is a better way to get the reassurance you need than asking her to stop doing something she obviously enjoys.
Does seeing your wife enjoying herself make you feel badly? If so, you really do need to question if poly is for you, since a BIG part of being polyamorous is cultivating enjoyment at the pleasure your partner has in being with other people.
Do you know her boyfriend personally, and have you spent any time getting to know him? I suggest you talk to him, or go for coffee -- not with her present but just the two of you. I know it's tough for guys to do this, but perhaps seeing him as just another person who is in fact different from you (and therefore not competition because you both offer her something different) might be reassuring.
I can think of more things to suggest, but my main advice is to take things slowly regarding your feelings, and to try to avoid vetoing while your wife is experiencing NRE with her boyfriend. I've seen this tactic backfire more often than not, creating hurt, anger and estrangement when really all a couple needs to do is give each other more reassurance and faith that things can be worked out.