Am I just a horrible person?

I would just see the attraction to this other guy as a symptom of your relationship not being quite right. I wouldn't leave your partner for someone new - as you say, it probably wouldn't work out anyway! He'd definitely be a rebound.

But if you're not happy then it's ok to end it just to be alone. Two happy homes are better for a child than one miserable one! Your child is so young they'd literally never even remember you being together.

Leave your relationship if you're unhappy and desire more, not for another man. Staying together won't be what's in the best interest of your son if you're unhappy. And it won't ruin his life to split. Being in a home with no love will for sure have an effect.

I wouldn’t risk a good father for a fling. That puts your baby in a horrible situation. Spend some time taking good care of yourself. And it doesn’t make you a horrible person for having these feelings but it would make you incredibly self centered to act on them. You don’t have to stay with your partner but don’t leave your kids dad with a bad taste in his mouth about you. Be respectful and break it off if you want as I agree that a romantic life is a huge part of a relationship. Try your best to make it romantic these next few months and see what’s killing the vibe. Also the first year is really hard on any relationship but regardless talk to your partner and if you want to break it off. No shame. Just don’t cheat.

Unpopular opinion probably, but your little one is only 5 months old. You've got a LONG road ahead of you yet and lust dies super quickly. Sometimes I feel like women on this app are far too quick to say 'dump him'.
Personally, I would maybe have a discussion with my partner about needing to feel more desired or whatever but totally forget the other guy. You need a supportive and comforting partner and your child needs a father far more than you need some dick 😅
BUT I don't think at all you're a horrible person, there's just an unscratched itch there and we all have needs!

You should be leaving him regardless of this other bloke. You’re not happy, that’s the bottom line! You’re not going to ruin your child’s life for separating, you need to model to your child the love and type of relationship you one day hope they’ll have, and being with someone that you’re not happy with isn’t the one! Be brave. Don’t leave him for this other man, but leave him because you’ve admitted yourself, you’re not happy

Have you had his testosterone levels checked?

I’ll try to make this short: I got pregnant the first time I had sex with my partner. He is my dads best friend I have know for many years but only had just started to “date” him. He’s younger than my dad but we do still have an age gap. He is an amazing man! Fast forward to our baby is now 9months old. Our sex life isn’t the best due to his daily medicine and what we like in sexual experiences but we both are attracted to each other and we try to improve. However we also have many general differences so I wonder if this relationship was even a good idea. But again he is an amazing man. I personally think that communication is sooo important. You should communicate your feelings. As time goes on and older couples I’ve talked to always say their relationship lasted longer because they were friends. Now I’m not there to see how these arguements are BUT I think it’s worth it to try to communicate your feelings and see how that goes for at. It’s natural to find others attractive and want

Relationships are never perfect. Weigh your options and again try to communicate and give him and yourself a chance to find that spark. But I do agree with the others when they say your baby is young and a happy split home is better than a unhappy together home.