Why does he get hard when giving me a back massage?

Is it a problem that he got an erection?

As most of the other responders indicated men can get an erection if the wind blows right. Being in close proximity to a woman and in a fairly intimate situation is certainly going to have some sort of effect. That doesn't make it wrong.

It probably would take a lot of training or practice to not have an erection. For me I never stop trying to have an erection. I talk to many men who as they get older regret that they can't get an erection. If we train ourselves to not have erections then that will happen in the long run. I have the great pleasure of getting erections all the time and I love it. They don't always come up when the situation is purely sexual either.

You must be a hottie, otherwise most men would not think much about it. I mentioned earlier that unless a man is a professional massageur, he will most likely get fired up at touching a woman like this. I went thru physical therapy training back in college and worked with many women volleyball players for a tournament to make a grade. I had to completely focus on what I was doing otherwise my ding-a-ling was going to get wild. Only thru training did I make it thru. Massage therapy is the same way, they teach you how to avoid this scenario as married people WILL invite you if your skill is good enough.

So this does not surprise me that he got hard, it means he is a straight man who likes women. No man sober gets fired up over ugly women so pay it no mind and be happy that you have the charm.

Bigger question. If you are married, why are you allowing another guy to massage you when you are half naked in the swimming pool? Or why are you alone with him on a couch? And thirdly. What are you looking down at his crotch for? Men are sensitive creatures when it comes to touching a woman. We are highly visible as well. But when you allow a man to combine those two features. He is going to get excited. Any man that finds a woman attractive is going to jump at the chance to rub oil or lotion all over her naked body. It won't always matter if she is married or not. Bodily responses are just acts of nature that couldn't be controlled.

My suggestion for you is to realize that this guy is most likely very interested in you, and the things you are allowing him to do to you, may be sending him a mixed message. If you don't want him excited around you, try hard not to give him excuses to get that way.

Its just how a guy works, no big secrets

Obvious you allowed him to touch you, I'm sure it was inviting to him for your desire "to be touched by him"

If the wind blows right I get and erection, I'm sure the same is true for 95% of guys our age

What happened on the couch? Did you look at him a certain way? Where you flirting?. I will tell you this, resist the urge to advance, save your self the drama down the road

Touching a woman anywhere gets a man excited. Others may be able to hide it better then some. Your friend obviously couldn't hide it.