Have you ever had a relationship that went bad shortly after saying I love you? i want to hear stories!?

I just wanna relate to someone. I've been with my boyfriend for a year and our relationship has been great for the most part. He finally told me he loves me like a month ago. Now things are starting to get sour not because he told he loves me I love him too. But because I'm starting to not trust him. I caught him lying to me about smoking weed I told him I don't care if you do it just don't lie and he continues to lie to me about it. And he's just been acting shady in general. Joking about calling an ex. One day he left work (we work together) with out even saying bye or anything. And he just makes insensitive comments. There is also this married skank that likes to flirt with him at work who has been texting him and he hasn't told me about it. I'm in a constant state of relationship anxiety. I'm starting not to trust him. He's 29 and I'm 25. I hate to break up with him because our relationship just hit a high point. Can anyone relate? Did you end a relationship shortly after saying I love you?