Sure hes not married?

I know you say you love him etc etc, but if you were seeing someone as well as him, how would he react? Would he be angry and consider it cheating? Or is it fine for you to see other people? Is the relationship between you exclusive? Or is that not defined either?
I would just feel like he is waiting for something better to come along. After all if he thought you were that important to him, he wouldn't want anything to get in the way of that, or lose you to someone else.

He’s just not that into you.

There is a book with this title too, get it and read it.

What do you want? Does he know what you are expecting? It is not a problem that he doesn’t want to define your relationship - unless it is a problem for you. It was never a problem for me until we talked about having kids. Then I wanted something more defined (permanent) before I would be happy to make a decision affecting my life and future. Decide what you need/want, and then let him know. Be prepared to accept whatever answer he gives you, even if it means you can no longer hang around waiting for him. Good luck 💗

I'd be telling him to shit or get off the pot. You're wasting time babe x

You're his doormat!!
Tell him to put up or F off.
You deserve better!!!

Awww darling. He's taking you for a ride. Ditch him.

15 months, I’d expect some kind of definition. It strange he doesn’t want to. Does this make him free to see others if he hasn’t actually made any sort of commitment to you? It daisies some red flags TBH.

I know a male colleague doing this same thing to some girl he sees. He is enjoying being single and is looking for someone better.

Not sure, what sort of relationship have you been having? Have you met his friends and family? Do you live in each other's lives a lot or is he keeping separate? Do you go out in public together and do things like hold hands? Are you friends on social media? Are you in any of his online photos?

If you haven't met friends and family and don't see him except for dates, he may be reluctant to commit.
If you are a big part of his life and you've met the people important to him, perhaps he is just taking it slowly. Has he been burned before? Are there big unanswered questions in his future about where he will be and what he'll be doing, like a deployment or the possibility of an interstate job?

Ask? Talk about it. If he won't then take a look at the bigger picture and decide if this is what you want