There's nothing you can 'do' to make anyone interested.
Just be yourself and stop trying too hard.
You should be aware that in a relationship the sparks will not last. It's called going through stages. The longer you stay together, it is realistic to expect to get tired of each other.
Firstly, mind yourself first. Take interest in something, like hobby or a career. Keep yourself busy with something else other than him.
Read, go out, spend time with friends, family, etc.
You have to keep yourself sane in the first place. Stop revolving your life around this guy.
Secondly, you may take interest in his interests.
Like sometimes, just face it, he's just not that into you. But it doesn't mean it's the end of the world. It just means time to take interest in other things before you catch up with each other again. After all you are two people, completely different, there is no such thing as 'two souls become one' or whatever similar so-called romantic rubbish.
- take interest in his hobbies, be curious, ask questions
- ask him what he likes to do and ask if you could join
- talk and let him know how you feel
- talk and ask him how HE feels
- be friends again... not lovers
It's normal that it feels mundane and bored at times, but that doesn't mean it has to ruin the relationship. It's all a matter of teamwork.
If even after you've given him space he still doesn't seem to want this anymore. Then let there be no drama. You may as well move on.
If it wasn't love in the first place, it will never be love 3 more years down the road. Or any time in the future for that matter.