I'm a 32M and have had this issue for well over 10 years but it's getting slightly worse and definitely not improving.

I love sex, my girlfriend does to. We've been together for a long long time (about 15yrs) and sex has always been amazing. That being said, when the evening comes and we have time for some fun, I don't feel like it. I often feel too tired, almost too lazy, to do anything. I find my girlfriend very attractive, even after so many years. And we've had discussions about opening our relationship to some extent which I am fine with but I don't particularly want to see other women, fearing the same thing will happen. It's obviously been causing some friction in my relationship and I'd like some tips to get past that, if anyone else has ever been through something similar.

A few details: I've seen a psychologist (Depression) and spoke to her about it a little. I started seeing a sexologist but only had 2 appts so far. No other known health issue and had my blood tested a few times for this reason over the years. I'm open to questions if it will help.

Thanks in advance.