Am I going through major relationships issues

So this lady my fiance works with he had become friends with and I thought they were doing something at one point cause he was always going out and be gone for two hours or so and then come back home to me. We have moved to a apartment closer to his work and now he's kind of relying upon me to do the driving mainly he hardly goes out plus he told me that the woman smokes meth that she had told him. Yesterday morning when I picked him up from work we ended up passing by and the guy that he that was with her my fiance was kind of laughing about and it was a really great done we got alot done we talked and everything but when I looked at his text messages she sent him a message f*ck you (fiances name) in which he didn't read it and this was after the drive by. Should I be concerned of her being jealous or should I have the mentality he's coming home to me and my daughter every night to forget her?