If Aries lost interest in you, it was because he was bored. It seems incredible that you do not know what Aries is like, and that it needs a constant adventure. Aries is always a person who loves love dramas, even if it is hard for them to accept it. He is never afraid of love and his feelings, Aries is not a person who is afraid to say what he feels for you.
But he is also a very impatient person, when he wants something he wants it at the moment, not before, much less after. And if you didn't give him what he wanted when he wanted, he probably lost interest in you for that very reason.
Besides, he also very much hates having to go after someone, having to remind him of everything he has to do.
And if he sees that you are not sure and that you are dragging yourself too much, he will be disappointed by that lack of interest and determination when it comes to showing your feelings.
Yes, it is true that Aries likes to fall in love a lot and that they love being around people, but they do not need anyone to be happy. He is a person with a lot of confidence in himself and with an overwhelming force. Aries does not wait for anyone in his life, he does not look for his 'better half', he does not want a person who steals his freedom and who is watching him / her all day.
If you really want to keep Aries interested, you need to show that you are a respectful, strong person, with a lot of self-love and a lot of security.
Aries does not need a person who is a 'lapdog' to go wherever he goes. If you don't want him to lose interest in you, you have to love Aries with true passion, but also with a lot of respect. Otherwise, Aries will take any opportunity to say goodbye to you.