I see this line everytime I pass Mcdonald's, day by day I'm used to it. But at first sight, I was not. I never had saw 'love' is used in prsent tense. I have thought it's only an ad twist.

So, is it right in terms of syntax? Is it acceptable in writing? It's colloquial or formal? What does it mean exactly?

Same questions with 'I will be loveing it'--if I coined this after that.

Thx.

Callithump

I’m learning English. If u find anywhere I can improve my composition, Pls do let me know. Bow.

Callithump, since you are learning English and ask for feedback on your writing, a few notes about your post and a reply to your question.

1. The expression "day by day" means "one day at a time", as in various mottos of support groups, "Day by day we grow stronger, wiser, etc." It is not an expression used in everyday speech. I expect that what you mean is "every day", which means just what it says.
2. "I never had saw" is incorrect. The construction is incorrect and the tense is incorrect. What you mean is, "I have never seen." The verb "see" is conjugated, present tense "I see", past tense "I saw", present perfect tense "I have seen", past perfect tense "I had seen". The tense you want in this context is the present perfect.
3. "I have thought" is correct as to construction but again not the correct tense. The present perfect is not what you want here. Better would be the past tense, "I thought", which is how it would be put in speech.

The expression, "I'm loving it!" is adwriter's language. It is grammatically correct, but not what anyone would say in formal or colloquial speech. It's a cute way of saying "I love it". Grammatically, it's the present progressive tense, which is a construction of "I am, he is, you are," etc., with the present participle of a verb, and denotes an action which is actually in progress as you speak. For example, someone calls you on your cellphone while you are at lunch and asks what you are doing, you would reply, "I'm eating lunch", meaning, "I am, at this moment, while we speak, in the act of eating my lunch."

Hope this helps.

You're doing well, by the way.