My husband seems to always check out men and mentions their clothing. He likes fresh cut flowers, rarely makes sexual advances and doesn't get hard when caressing me. What do you think?

Let me see, he likes fashion, he likes flowers, if he liked Justin Bieber then there would be no doubt. ( LOL ) sorry but the silly examples have nothing to do with it, many gay men are buff and would not know fashion and hate flowers, maybe car mechanics, brick layers and so on.
You have some silly TV theme of what you think gay may be like.

He may not be sexually aggressive and may have issues having an erection. Many men do.

Wow! Talk about stereotypes! None of that means he's gay. Reread what Fr_Chuck wrote.

A man that nev comments on sexy women is unusual...

I'll introduce you to my fil, husband, two sons, two brothers, and about 100 other males I know.

The only way to know anyone's sexuality is to ask. Even catching someone 'in the act' only narrows it down to bi-sexual.

How long have you been married and was he like this before you married him? If you have always had questions about his interests, why did you marry him? If his interests changed, did something happen besides the wedding?

Have you had an open and honest discussion about sex and what both of you like and dislike? Has he expressed a preference for you to be the assertive one in the relationship?

As for not commenting on women, he may think that to comment on other women might offend or upset you. Ask him.

Sounds like you hung around a lot of rude men that were not taught proper manners.

Many men will joke or talk about women around other men, but never around women and most certainly not around a wife or girlfriend, A real man would be considerate of his wife feeling and not talk about other women in front of her.