Do guys, even if there in a relationship, get hard for other women?

I have a male friend at work who I have lunch with along with others and he has a girlfriend and he always seems to not make eye contact with me by either looking away repeatedly or go on his phone. I thought he doesn't like me but then he keeps saying he had a great chat (even though he doesn't engage) and that he'll see me again for lunch next so I don't think its that. Best reason I can come up with without sounding to self-centered is he finds me attractive and may feel bad since he has a girlfriend. What do you all think?
Do guys, even if there in a relationship, get hard for other women?
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