<human>: Can you condense the text into a few key points?

Him (26) and his girlfriend (24) have been in a long term relationship for 3 years now and she wants a break! So they both agree to have a break. 

They are open to each other and both said that they are talking to other people about sex on their break, they have both made it clear that they can sleep with other people so long as they don't tell each other who and when etc. 

I (23) am friends with both of them and have been the one of the people hand full of people in our social group that they both talk to about it but lately he has become sexual with me and wants to have sex with me when they are on the break! He says he has feelings for me and would be chasing me if she was out of the picture but he is still loves her (obviously). 

Im curious to actually having sex with him but I don't want to feel guilty, when they get back together (which could happen) and I have to look at her in the eyes knowing I slept with him. 

Am I in the wrong for even thinking of doing anything with him even when she said he could do whatever on the break?
<bot>: Should I meet up with him and us have sex when he is on a 3 week break from his long term relationship or is he just using me for the thrill?