Breakup After Being In A Relationship For 4 Years

As I write this.... I'm filled with so much hurt and regret. 
My girlfriend whom I thought would be patient enough for me so I could get married to her has broken up with me.
I met her while I was writing my final year project in Yabatech about 4 years ago. We were cool together and the distance between us didn't mean that much to me even though she stays in ikorodu and I stay in surulere. The problem started when I gained admission to Unilag due to my decision for self development. I'm 31 years old and she is 25.
During the last 2 years I noticed she has changed drastically I notice that she now has stuffs like new shoes and new bags. Which of course ordinarily she wouldn't have been able to afford. The only time we see is on weekends and that's because she is still in Yabatech schooling and sometime when she comes like that she acts funny with phone calls. The way she talks to some certain people so suspicious. But none the less she always feels cool with me and always wants to be around me. Could it be because of sex?

I noticed that she behaves single at school and even on social media. We do not chat or use social media, we added each other but at a point I had to take her off because she doesn't portray any thing that shows we are actually dating...i took her off all platform of social media and she wasn't perturbed about it. I don't actually know what's going on in school or her place of residence but I have a very strong feeling that she has been cheating on me and some other guy have been buying her things I can't get for her. But on top of this she was actually looking for school fees and I was deploying all methods to make sure she pays this on time and that alone made me confused!. We had a heated argument on Sunday and she was yelling and talking back at me... I left the house for her in annoyance only for me to come back and she is gone. She left a note that says that she is no longer interested. Guys please what should I do. I love this girl so frigging much. I can't sleep or think straight right now. It's almost impossible for me to start all over again. I feel hopeless. Please guys your advice!