When a disillusioned married woman is absorbed by a surrealist painting, she struggles to develop the power to free herself from the painting before becoming part of it, while falling in love with a man of painting.

The event that motivates her to take action is getting trapped in the painting, as a response to that, she needs to find a way back to reality - this makes sense. Therefore, the inclusion of the love story, in the context that you've established, is superfluous.

What's the main story line in this concept? The love story? Or her getting back to reality?

Your corrected version: This is the corrected logline, the original logline is:
In an exhibition, after a woman enters a painting, her boyfriend must look for the painter before he leaving the exhibition.

Your initial logline was better. This is incomplete and does not reflect any plot.

For the initial logline:
If you have established your character in reference to your logline, you must be good to go. You mentioned that you are yet to master English, that's the only thing I suggest you do the earliest.
The initial version is good.

Richiev offers a good movie as an example to compare with this one.

In the "Wizard of Oz" Dorothy is never so enraptured with anyone or anything in Oz that she would be tempted to want to stay.? From the git go, her unalterable goal is to get back home.? But she doesn't know how, doesn't have any means of getting back.? The story is set up so that she must contact an enabler, someone with power to get her back home.? So her specific game plan to get back home is to persuade the Wizard to make that possible.

A logline for the movie might be something like: "When a tornado transports a young Kansas girl to a magical kingdom, she must persuade its all-powerful Wizard into enabling her to go home." (24 words)

(Well, of course, come to find out he's not all-powerful.? That she's had the means all along to get back home -- the red slippers.? ?But a logline is written from the perspective of what the protagonist knows at the time she commits to her objective goal? -- not what she eventually discovers.)

In contrast, the logline for this premise provides us no clue as to her game plan to get back to the real world.? Dorothy must convince the Wizard. What, specifically, must the protagonist in this logline do?