"there's no real reason there should be so much tension between us"
Tension can be broken if you/they start talking! It's probably not as bad as you think. What you haven't explained (or maybe I wasn't reading closely) was 'how/why' are you different than the team? How are your 'close' friends different? Is it just the fact they are knobs with the ladies? That can be humorous and maybe you can help them in that department, maybe even find common ground and they'd appreciate your input on that. Be friends with who you want to be friends with though. If those teammates are so adamant about including you and making you feel as part of their own, they would have done so by now. Also, I don't think there's anything wrong with you just simply telling them, "hey guys, thanks for the dinner invite, but I'm having dinner with my lax buddies". It's the truth anyway and there's nothing wrong with it. XC athletes are cliquish. My HS varsity was that way and now that I look back on it 14 years later, I wish we would have been less cliquish. College was similar, but those who chose not to participate in all the team functions were not looked down on. It was college, we all realized folks on the team had more to do than just run and study and we welcomed those differences. If someone kicked ass, but weren't part of the 'team social' life, we'd still invite them out, showed interested in what they liked/disliked. But if they simply didn't want any part of the non-running stuff the team participated in, than we didn't force it on them. Good luck to you, hopefully you'll have good memories of these years when you get older!