1- “Actually I’m not so sure…”
Girls won’t be happy with they hear it. It seems like your haven’t thought it through to spend your life with her. It seems you don’t even know what you want, so how can she happy with what you ask?
2- “I thought I would find my perfect match, but I realized…”
As you mention, it means she is not your perfect match, she’s not the one you want to find. Usually when she hears the first irritating sentense, she won’t hear anything afterwards. Remember, every girlfriend wants to be someone’s the one, soulmate, perfect match!
3- “Although my marriage failed before, I’m really serious this time…”
Don’t mention about ex-girlfriend, ex-wife, or anything related to the former relationship. She is the partner you want in the future. Let it go!
4- “Look! I propose to you now, are you ok now?”
Sounds like you propose unwillingly eh? Some couples have marriage plans already, so proposal seems just like a play that satisfy your girlfriend. But come on! Every woman wants to see her man’s sincerity! It’s a life-long commitment, how can it be too casual?
5- Discuss about the engagement ring
Unless you have a 10 carats diamond ring, or please don’t discuss the size or the price of the ring. It will make her compare the ring with other friends.