You can say that King Solomon loved intensely. First, the Bible says that he loved the Lord (1 Kings 3:3). He brought as many as a thousand animals as a burnt offering, which is the sacrifice of devotion. However, later it turns out that his passion had focused on a thousand others, namely foreign women (1 Kings 11:1).
The attention of Solomon's heart, his affection, was first completely on God and now completely on commerce and sex. That did not happen overnight; it was an insidious process. Where your treasure is, there your heart will be too (Matthew 6:21). See how often 1 Kings 11:1–9 talks about the heart.
Why didn’t God stop him? 1 Kings 11:9 says that the Lord appeared to him twice. The first time was after those thousand sacrifices that Solomon had made (see 1 Kings 3:1–28). In 1 Kings 9:1–9, God spoke to him again after he had finished the temple and all his buildings. Then God warns him, telling him in particular about the disastrous consequences of serving other gods.
11 Therefore the LORD said to Solomon, “Since this has been your practice and you have not kept my covenant and my statutes that I have commanded you, I will surely tear the kingdom from you and will give it to your servant.