Translation - English-Latin - tell someone you love them

Hi Alex!
You know I have some doubts regarding yor translation of the second sentence.

1. I haven't met such an expression "certum habe", Alex. My proposition:

-->pro certo habe = know for certain, be sure

2. Tum --> ergo, igitur?

3. te illum amare --> te eum amare/in amore habere/
("illum" would refer to the 3rd person)

4. You know I would try to avoid this double ACI:
te alicui dicere --> ut alicui dicas

What do you think?

Hi Aneta!
Sorry, I found this one quite difficult to be translated...

1. You're right, the expression is pro certo habere.

2. I guess it can be changed with ergo. Do "tum" and "ergo" have different meanings?

3. I used illum to underline that it is referred to the previous alicui. I thought that eum was too general. Is this wrong?

4. Yes, I also wanted to avoid two consecutive infinitive propositions. But, while in Ancient Greek you can always replace an infinitive proposition with a declarative proposition (introduced by "ὡς" or "ὅτι" ), I don't know how we can do it in Latin.

Teach me, please.

Don't worry, dear. The sentence was not so easy to translate into Latin.
Ok, let me try to answer some of your questions.

1.

2. tum = then, at that time, next, moreover, besides
Ergo/igitur= therefore, consequently, then, so

3. Have a look at the following sentence from the Bible: "Providete mihi aliquem bene psallentem et adducite eum ad me".

Both pronouns ("is, ea id" and "ille, illa illum" ) are actually similar and we can often exchage them, but in sentences like this above we have to use “eum”, because “illum” would be confusing and somebody could understand that “illum” didn’t refer to “aliquis” but to somebody else...
Generally:
Ille = that one
Is =this one

4. Why are you asking me how to do it? I have just done it for you in the former post
te alicui dicere --> ut alicui dicas

So, I would let it go as:
"Tum certum habe te alicui dicere te illum amare".
--> Ergo in certo habe ut alicui dicas te eum amare (in amore habere).

OK. Thank you!

My pleasure, dear Alex.