Why does this always happen?

Every time my boyfriend and I are doing great, there is always someone that comes along and feels like they're my soulmate. Usually I keep them around as friends because I'm not into cheating. So we agree to stay friends and I mean these people are just like me and every time we are done hanging out...it leaves me questioning if I'm in the relationship with the right person after all and I hate it. So I quit doing it. I've been fine. But, all of a sudden I meet another person again and I start opening up to this person with my secrets and concerns and turns out he has the same view on tons of things and I just feel right with him. We kissed and I didn't stop it and I just feel so much more passion when I kiss him and with my current boyfriend I've never felt that. I just have no idea if this is a sign or what.