When embarking on a new relationship, each person brings along his or her own baggage from previous relationships, and that includes their friends. But there's no guarantee that although you and your mate are compatible, that you and his friends will be compatible. First, it's important to consider where they're coming from. He went from drinks with the boys to romantic dinners with you; it's natural that there may be some resentment toward you for usurping his guy time. Perhaps they miss his ex and don't want anyone to take her place. As difficult as it may seem, it's possible for you all to get along - and maybe even like each other along the way. The first rule, above all, is never to try to drive a rift between your mate and his mates. Keeping them from seeing one another will only lead to resentment all around. But if you find that your guy is reserving most of his nights and free time for spending with his guy, then that could be a sign that his bromance is taking precedence over your romance.
Then it becomes time to sit down with him and have a talk, but be sure your expectations are realistic. If your guy needs his time with the boys, then give it to him - after all, it'll give you the chance to have a ladies' night. As for getting along with the guys, there are a few ways to go about it. Time usually heals that jealousy they may feel for you, and spending some quality time with them just may help. Remember that it's probably not you who they don't like - it's the lack of time they now get to spend with your guy. A great way to smooth the waters is to get a couple of girlfriends in on the action - perhaps a few of the single guys and girls in the group will hit it off. That sets up a great opportunity for double dates and group fun in the future!