Am I obsessed with another man?

Hi everyone,

I need your advice, I feel like this is going to be a long one, but I think you need the background... so bear with me!

I have been with my husband for more than 10 years now, we have one daughter together, who is 4, and his son, who is 15. We have a great life, we loved each other madly when we got together, and then things just sort of slipped from there. Having our daughter changed our relationship, then my mum passed away very unexpectedly and that affected our relationship again. We started going to therapy and been going for a year now.

In this time, I have become really close to my personal trainer - I know, what a cliche! I have always loved working out and going to the gym, and in the last year or so I found a trainer I really clicked with, anyway... we now message each other a lot, we often text for hours late at night, we just get on so well when we are together. I now flip between being madly obsessed with him sexually and then thinking I am mad and I need to be realistic, we're both in relationships and this is just a friendship.

I am not saying I am in love with him, I am by no means thinking I'd leave my husband for him, but my god, the sexual attraction just come over me and I feel like I can't think straight anymore.

In a way I think if we just had sex once, then everything will just sort of fizzle out, and I should just do it and get over it. But you can see how the situation is just crazy complicated and I don't actually want to hurt anyone involved. Also, I don't even know if he feels the same... sometimes I feel like I am going crazy? I mean, you don't spend hours late at night, messaging someone if there isn't something there, right?

But am I obsessed with him cause things are not great with my OH, or because je's just fit, or what is it? Am I just going mad and this is all in my head?

Has this happened to any of you? What did you do?