First of all...a BIIIIGG Grandpa hug to you!
It hurts to read your story, BUT your story is not unique, it happen several times each day around the globe, that one part hurt the other by infidelity.
Since most of the time a such action include one of each sex, it is wrong to start to not trust the males or females as group, but more start to evaluate your relationship with your partner.
In order to go on in a partnership after such an experience, call for an absolute forgiveness, else your doubt will destroy the relationship over time, and also your ability to love, because you don't have the trust anymore.
By us not trusting our surroundings (relations) we create a negative environment.
This will lead to more discussions, and blames are easy to be thrown, which again might lead to more and more depressions, because our energies are vanishing, and we don't get those positive impulses to get it back.
A person who trust his/her partner allow him/her to do a lot more (inside our rules) then one who have got doubt.
A relationship that shall function need to build on mutual respect and care for each other, and the wish to grew old together.
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Another Biiig Grandpa Hugg and then over to my recommendation.
You are 19, and you both have been together for 3 years.
When you fell in love with him in an age of 16 you both was still "kids", and in a time period where we develop much more each year, then later in life.
I think the boy you might have had a crush on in the start, haven't develop in same speed as you, he might still want to fool around...he might still not want to have any commitments, but on the other side he might not want to loose you either, he will have it all.
I ask you to evaluate your situation, and hopefully end it, in an age of 19, I can't see that this relationship can be a fruitful one, for the ages to come, and by ending it, he might do a serious decisions to change....but don't give him much time.
Many are afraid to end the relationship because they are scarred to be alone, they feel defeat, they make pink thoughts about everything will become better....often it will not....it is just "waste of time".
Don't hate him, don't hate the females, just take it as one of life's lesson, if you are coming through this, then you are coming out stronger, and life is like a rose....it has beautiful flowers, but if you grab the stalk you will be hit by its needles, first time it will be easy to be hurt...next time one are more aware....but the flower is so nice that life must just be enjoyed, even if it hurts now and then.
By ending you relationship, you get rid of the cause for your worries about him, you will again be able to focus on the positive around you, you might start to live and be happy again....and suddenly a new prince will be by your side
Good luck ...and another Hug
