Firstly: 

It is permissible for the spouses to be intimate with one another, so long as they are certain that there will be no emission of maniy, because of the report narrated by al-Bukhaari (1927) and Muslim (1106) from ‘Aa’ishah (may Allaah be pleased with her) who said: The Messenger of Allaah (S) used to kiss and touch (his wife) when he was fasting, but he was the most able of you to control his desire. 

If a man is intimate with his wife without having intercourse, then one of the following two scenarios must apply: 

1 – That this intimacy leads to emission of maniy. In this case the fast is invalidated and the one who emitted maniy must make up that day. 

Al-Nawawi (may Allaah have mercy on him) said in al-Majmoo’ (6/349): If he kisses her or is intimate with her, without having intercourse, or he touches a woman’s skin with his hand or otherwise, if he emits maniy then his fast is invalidated, otherwise it is not. The author of al-Haawi and others narrated that there was scholarly consensus that the fast of one who kisses his wife or is intimate without having intercourse and ejaculates is invalidated. End quote. 

Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said: If a man is intimate with his wife by touching or kissing the face or touching the private part (without having intercourse) and he ejaculates, then his fast is broken, but if he does not ejaculate then the fast is not broken. End quote. 

Al-Sharh al-Mumti’ (6/388). 

2 – If that intimacy results in emission of madhiy, in this case the fast is not invalidated. 

Shaykh ‘Abd al-‘Azeez ibn Baaz (may Allaah have mercy on him) said: If a man kisses his wife and is intimate with her without having intercourse whilst fasting, all of that is permissible and there is nothing wrong with it, because the Prophet (peace and blessings of Allaah be upon him) used to kiss his wife when he was fasting, and he would be intimate with her whilst he was fasting. But if a man fears that he will fall into that which Allaah has forbidden because he is easily aroused, then it is makrooh for him to do that. If he ejaculates then he must refrain from eating and drinking for the rest of the day, and he must make up that fast. But he does not have to offer any expiation according to the majority of scholars. As for madhiy, it does not affect the fast according to the more correct of the two scholarly opinions, because the basic principle is that the fast remains valid and is not invalidated, and because it is too difficult to avoid it. And Allaah is the Source of strength. End quote. 

Fataawa al-Shaykh Ibn Baaz (15/315) 

Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) was asked about a man who was intimate with his wife when he was fasting, and he emitted madhiy; what is the ruling on his fast? 

He replied: If a man is intimate with his wife, and he emits madhiy, his fast is still valid, and he does not have to do anything according to the scholarly view which we regard as correct. That is because there is no evidence to suggest that this breaks the fast, and it is not valid to compare it to maniy, because it is less than it. This view which we favour is the view of al-Shaafa’i and Abu Haneefah, and it was favoured by Shaykh al-Islam Ibn Taymiyah (may Allaah have mercy on him) who said in al-Furoo’: It is more correct. And he said in al-Insaaf: It is the correct view. End quote. 

Majmoo’Fataawa Ibn ‘Uthaymeen (19/236). 

For more information please see the answer to question no. 37715. 

Thirdly: 

If a man is confused in this case and is not sure whether what has come out of him is maniy or madhiy, in most cases it is probably madhiy, because madhiy is that which is emitted when one is intimate, and the fast cannot be judged to have been spoiled on the basis of mere conjecture. 

The difference between madhiy and maniy has been explained previously on this site, in the answer to question no. 99507 and 2458. 

And Allaah knows best.